I think that was intentional. Remember, one of the girls in the movie (or maybe Franco's character, don't remember) said: "This is like playing a video game." And the ending is literally what would happen in a video game! Plus there are a lot of repetitive scenes, neon colors etc, which give viewer the impression of being high just like characters were.
And Franco's interpretation was again intentional - it was meant to be over the top.
But of course, this movie is just very much and may not be everybody's cup of tea.